Split attachment paths (#848)

* fixed attachment statistics for sqlite

* Split attachment path into internal and external path, so the external source URL can be retained after a file is downloaded

* Make internal and external path for attachments nullable, to make clear that they have no internal or external path

* Added migrations for nullable columns for postgres and mysql

* Added migration for nullable internal and external pathes for sqlite

* Added translations

* Fixed upload error

* Restrict length of filename badge in attachment edit view

* Improved margins with badges in attachment edit

* Added a link to view external version from attachment edit

* Let media_url  stay in API attachments responses for backward compatibility

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Co-authored-by: jona <a@b.c>
Co-authored-by: Jan Böhmer <mail@jan-boehmer.de>

src/Services/ImportExportSystem/PartKeeprImporter/PKImportHelperTrait.php

@@ -105,7 +105,7 @@ trait PKImportHelperTrait
         //Next comes the filename plus extension
         $path .= '/'.$attachment_row['filename'].'.'.$attachment_row['extension'];
 
-        $attachment->setPath($path);
+        $attachment->setInternalPath($path);
 
         return $attachment;
     }